Vanadium-containing residual fuels modified with zinc and alkali metal compounds



leum fuels. clermg non-corrosive those residual fuels which containVANADIUM-CONTAINING RESIDUAL FUELS MODIFIED WITH ZINC AND ALKALI METALCOMPOUNDS Albert G. Rocchini, Oakmont, and Charles E. Trautman,

'Cheswick, Pa., assignors to Gulf Research & Developmeut Company,Pittsburgh, Pa., a corporation of Delaware Filed Apr. 16,1958, Ser. No.728,904

6 Claims. (Cl. 60-35.6)

This invention relates to vanadium-containing petro- More particularly,it is concerned with renfurnaces, boilers and gas turbines the ashresulting from combustion of the fuel oil is highly corrosive tomaterials of construction at elevated temperatures and attacks suchparts as boiler tubes, hangers, turbine blades and the like. Theseeffects are particularly noticeable in gas turbines. Large gas turbinesshow promise of becoming an important type of industrial prime mover.However, economic considerations based on the efliciency of the gasturbine dictate the use of a fuel for this purpose which is cheaper thana distillate diesel fuel; otherwise, other forms of power such as dieselengines become competitive with gas turbines.

One of the main problems arising in the use of residual fuel oils in gasturbines is the corrosiveness induced by those residual fuels containingsutficient amounts of vanadium to cause corrosion. Where no vanadium ispresent or the amount of vanadium is small, no appreciable corrosion isencountered. While many residual fuel oils as normally obtained in therefinery contain so little vanadium, or none, as to present no'corrosionproblems, such non-corrosive fuel oils arenot always available at thepoint where the oil is to be used. In such instance, the cost oftransportation of the non-corrosive oil to the point of use is oftenprohibitive, and the residual oil loses its competitive advantage. Thesefactors appear to militate against the extensive use of residual fueloils for gas turbines. Aside from corrosion, the formation of depositsupon the burning of a residual fuel in a gas turbine may result inunbalance of the turbine blades, clogging of openings and reducedthermal efiiciency of the turbine.

Substantially identical problems are encountered when using a solidresidual petroleum fuel containing substantial amounts of vanadium.These fuels are petroleum residues obtained by known methods ofpetroleum refining such as deep vacuum reduction of asphaltic crudes toobtain solid residues, visbreaking of liquid distillation bottomsfollowed by distillation to obtain solid residues, coking of liquiddistillation bottoms and the like. The solid residues thus obtained areknown variously as petroleum pitches or cokes and find use as fuels.Since the vanadium content of the original crude oil tends toconcentrate in the residual fractions, and since the processing of theresidual fractions to solid residues results in further concentration ofthe vanadium in the solid residues, the vanadium corrosion problem tendsto be intensified in using the solid residues as fuel.

The vanadium-containing ash present in the hot flue gas obtained fromthe burningof a-residual fuel containing substantial amounts of vanadiumcompounds causes catastrophic corrosion of theturbine blades and othermetal parts in a gas turbine. The corrosive nature of United StatesPatent; 0 "ice meme, ,jifififi the ash appears to be due to its vanadiumoxide content. Certain inorganic compounds of vanadium, such as vanadiumoxide (V 0 which are formed on combustion of a residual fuel oilcontaining vanadium compounds, vigorously attack various metals, theiralloys, and other materials at the elevated temperatures encountered inthe combustion gases, the rate of attack becoming progressively moresevere as the temperature is increased. The vanadium-containing ashforms deposits on the parts affected and corrosively reacts with them.It is a hard, adherent material when cooled to ordinary temperatures.

It has already been proposed to employ in corrosive residual fuels smallamounts of certain metal compounds to mitigate the vanadium corrosion.Such compounds are of varying effectiveness and it has not always beenpossible to reduce vanadium induced corrosion to a minimum amount.

.It has now been discovered that residual petroleum fuels containingvanadium in an amount sufiicient to yield a corrosivevanadium-containing ash upon combustion can be rendered substantiallynon-corrosive by incorporating therein to form a uniform blend (1) asmall amount of a vanadium-free zinc compound sutficient to reduce thecorrosiveness of the ash but not in excess of that amount which willyield about 4 atom weights of zinc ,per atom weight of vanadium in saidfuel, and (2) .asmall amount of a vanadium-free alkali metal compoundsu'fiicient to further reduce the corrosiveness of said ash to aminimum. In the fuel compositions of the invention the coaction of thetwo additive compounds is such that the corrosion is reduced tonegligible amounts.

In the accompanying drawing the single figure shows an apparatus fortesting the corrosivity of residual fuel oil compositions.

The type of residual fuel oils to which the invention is directed isexemplified by No. S, No. 6 and Bunker C fuel oils which contain asuffici'ent amount of vanadium to form a corrosive ash upon combustion.These are residual type fuel oils obtained from petroleum by methodsknown to the art. For example, residual fuel oils are obtained as liquidresidua by the conventional distillation of total crudes, by atmosphericand vacuum reduction of total crudes, by the thermal cracking of toppedcrudes, by visbreaking -heavy petroleum residua, and other conventionaltreatments of heavy petroleum -oils. *Res'idua thus obtained aresometimes diluted with distillate fuel oil stocks, known as cutterstocks, and the invention also includes residual fuel oils so obtained,provided that such oils contain sufiicient vanadium normally to exhibitthe corrosion characteristics described 1 by weight for some of the highvanadium stocks, ex-' hibiting severe corrosion.

The type of vanadium-containing solid residual fuels to which theinvention is directed is exemplified by the coke obtained in knownmanner by :the delayed thermal coking or flui'clized cokingof topped orreduced crude oils and by the pitches obtained in known manner by thedeep vacuum reduction of asphaltic-crudes to obtain solid residues.

These "materials have ash contents -of the :order of 0.18.

percent by weight, more or less, and :contain corrosive amounts ofvanadium when :prepared from stockscontainingsubstantialamountsofvanadium. Atypical pitch exhibitingcorrosive characteristics upon combustion had a softening point of 347F. and a vanadium content, as vanadium, of 578 parts per million.

Any zinc compound, organic or inorganic, which is free from vanadium isused as the zinc additive of the invention. Similarly, any organic orinorganic vanadium-free alkali metal compound is employed. The alkalimetals include sodium, potassium, lithium, cesium and rubidium; sodiumand potassium compounds are preferred. Such inorganic alkali metal andzinc compounds as the oxides, hydroxides, acetates, carbonates,silicates, oxalates, sulfates, nitrates, halides and the like aresuccessfully employed. In this connection, the mixture of salts presentin sea water, as disclosed in our copending application Serial No.654,812, filed April 24, 1957, comprises a suitable alkali metalcompound. Zinc oxide is a preferred inorganic zinc compound. The organiccompounds of zinc and the alkali metals include the oil-soluble andoildispersible salts of acidic organic compounds such as: (1) the fattyacids, e.g., valeric, caproic, Z-ethylhexanoic, oleic, palrnitic,stearic, linoleic, tall oil, and the like; (2) alkylaryl sulfonic acids,e.g., oil-soluble petroleum sulfonic acids and dodecylbenzene sulfonicacid; (3) long chain alkyl sulfuric acids, e.g., lauryl sulfuric acid;(4) petroleum naphthenic acids; (5) rosin and hydrogenated rosin; (6)alkyl phenols, e.g., iso-octyl phenol, t-butylphenol and the like; (7)alkyl phenol sulfides, e.g., bis(isooctyl phenol)monosulfide,bis(t-butylphenol)disulfide, and the like; (8) the acids obtained by theoxidation of petroleum waxes and other petroleum fractions; and (9)oil-soluble phenol-formaldehyde resins, e.g., the Amberols, such ast-butylphenol-formaldehyde resin, and the like. Since the salts or soapsof such acidic organic compounds as the fatty acids, naphthenic acidsand rosins are relatively inexpensive and are easily prepared, these arepreferred materials for the organic additives.

When employing in residual fuels the inorganic additives of theinvention, it is desirable to use finely-divided materials. However, thedegree of subdivision is not critical. One requirement for using afinely-divided material is based upon the desirability of forming afairly stable dispersion or suspension of the additives when blendedwith a residual fuel oil. Furthermore, the more finelydivided materialsare more efiicient in forming uniform blends and rendering non-corrosivethe relatively small amounts of vanadium in a residual fuel, whether thefuel be solid or liquid. The inorganic additives are therefore employedin a particle size range of less than 250 microns, preferably less than50 microns. However, where the inorganic additives are water-soluble,for example, in the case of zinc sulfate, sodium carbonate, and thelike, it is not necessary to employ finely-divided materials since, ifdesired, the additives can be dissolved in water to form a more or lessconcentrated solution and the water solution emulsified in the fuel.

The organic additives of the invention are oil-soluble oroil-dispersible and are therefore readily blended with residual fuels toform uniform blends. Since on a weight basis in relation to the fuel,the amounts of the additives are small, it is desirable to prepareconcentrated solutions or dispersions of the organic additives in anaphtha, kerosene or gas oil for convenience in compounding.

In the practice of the invention with vanadium-containing residual fueloils, the mixture of additives is uniformly blended with the oil in thedisclosed proportions. This is accomplished by suspending thefinely-divided dry additives in the oil, emulsifying or dispersing aconcentrated water solution of the water-soluble inorganic additives inthe oil, or dissolving or dispersing the organic additives in the oil.If desired, suitable surface active agents, such as sorbitan monooleateand monolaurate and the ethylene oxide condensation products thereof,glycerol monooleate, and the like, which promote the stability of thesuspensions or emulsions can be employed.

In the practice of the invention with the solid residual fuels,incorporation of the additives of the invention is accomplished inseveral ways. The additives can be suspended, emulsified or dissolved inthe liquid vanadiumcontaining residual stocks or crude oil stocks fromwhich the solid residual fuels of the invention are derived, and themixture can then be subjected to the refining process which will producethe solid fuel. For example, in the production of a pitch by the deepvacuum reduction of an asphaltic crude oil, the additives or aconcentrate thereof are slurried with the oil in proportion to thevanadium content thereof, and the whole subjected to deep vacuumreduction to obtain a pitch containing the additives uniformly dispersedtherein. As still another alternative, particularly with a pitch whichis withdrawn in molten form from the processing vessel, the additivescan be mixed with the molten pitch and the mixture allowed to solidifyafter which it is ground to the desired size.

In the case of either liquid or solid residual fuels, the additives canbe separately fed into the burner as concentrated solutions ordispersions. In such a case, it is preferred to meter the additives intothe fuel line just prior to the combustion zone. In a gas turbine plantwhere the heat resisting metallic parts are exposed to hot combustiongases at temperatures of the order of 1200 F. and above, the additivescan be added separately from the fuel either prior to or duringcombustion itself, or even subsequent to combustion. However they mayspecifically be added, whether in admixture with or separately from thefuel, the additives are introduced into said plant upstream of the heatresisting metal parts to be protected from corrosion.

The zinc compounds and the alkali metal compounds are both employed insmall, corrosion retarding amounts with respect to the fuel, and in suchamounts with respect to each other as to minimize the corrosiveness ofthe ash. In order to obtain the desired coaction with the alkali metalcompound, the zinc compound is employed in a small amount sufiicient toretard the corrosiveness of the ash but not in excess of an amount whichyields about 4 atom weights of zinc per atom weight of vanadium in thefuel. In larger amounts than about 4 atom weights of zinc per atomweight of vanadium, the coaction with the alkali metal compound is notobtained, the zinc compound appearing to act independently. With theamounts of zinc compound stated, the alkali metal compound is employedin a small amount sutficient to minimize the corrosiveness of the ash.For example, when the zinc compound is employed in the amount of 4 atomweights of zinc per atom weight of vanadium, ordinarily an amount ofalkali metal compound yielding about 1 atom weight of alkali metal peratom weight of vanadium is sufiicient to reduce the corrosion tonegligible amounts. In the compositions of the invention, an atom weightratio of zinc to vanadium of 4:1 and an atom weight ratio of alkalimetal to vanadium of 1:1 are preferred.

The following examples are further illustrative of the invention.

EXAMPLE I With a residual fuel oil uniformly blend 0.12 percent byWeight of zinc oxide and 0.02 percent by weight of sodium carbonate. Theresidual fuel oil employed has the following inspection:

The .resulting composition has an atom weight ratio of zinc to vanadiumof 4:1 and an atom weight ratio of sodium to vanadium of 1:1. Theadditives are stably dispersed in the fuel oil.

EXAMPLE II To a residual fuel oil, add and uniformly blend 0.63 percentby weight of a solution in naphtha of zinc salt of petroleum naphthenicacids containing '8 percent by weight of zinc and 0.6 percent by weightof sea water made up in accordance with the composition and preparationfor synthetic sea water shown in ASTM Test D665-54 published in ASTMStandards on Petroleum Products and Lubricants, November 1954, by TheAmerican Society for Testing Materials, Philadelphia, Pennsylvania. Theresulting'fuel oil composition has an atom Weight ratio of zinc tovanadium of 4:1 and an atom weight ratio of sodium to vanadium of 0.8:1.The residual fuel oil employed in this example has the followinginspection:

Melt a solid petroleum pitch obtained from the deep vacuum reduction ofan asphaltic crude. This pitch has a softeningpoint of 347 F. and avanadium content of 578 parts per million. While the pitch is in moltenform, add and uniformly blend therein 0.37 percent by weight of zincoxide and 0.1 percent by weight of potassium sulfate. Upon cooling andsolidification, grind the mixture to about 150 mesh. The resulting fuelhas an atom weight ratio of zinc to vanadium of 4:1 and an atom weightratio of sodium to vanadium of 1:1.

EXAMPLE IV To the same residual fuel oil of Example I, add and uniformlyblend 0.12 percent by weight of zinc oxide and 0.11 percent by weight ofa solution in naphtha of the sodium salt of petroleum naphthenic acidscontaining 7 percent 'by weight of sodium. The resulting fuel oilcomposition has an atom weight ratio of zinc to vanadium of 4:1 and anatom weight ratio of sodium to vanadium of 1:1.

Similar compositions are prepared employing the other zinc and alkalimetal compounds disclosed.

In order to test the elfectiveness of the additives of this inventionunder conditions of burning residual fuels in a gas turbine, theapparatus shown in the drawing is employed. As shown therein, theresidual oil under test is introduced through line 10 into a heatingcoil 11 disposed in a tank of water 12 maintained at such temperaturethat the incoming fuel is preheated to a temperature of approximately212 F. From the heating coil 11 the preheated oil is passed into anatomizing head designated generally as 13. The preheated oil passesthrough a passageway 14 into a nozzle 15 which consists of a #26hypodermic needle of approximately 0.008 inch ID. and 0.018 inch OD. Thetip of the nozzle is ground square and allowed to project slightlythrough an orifice 16 of approximately 0.020 inch diameter. The orificeis supplied with 65 p.s.i.g. air for atomization of the fuel into thecombustion chamber 21. The air is introduced through line 17, preheatcoil 18 in tank 12, and air passageways 19 and 20 in the atomizing head13. The combustion chamber 21 is made up of two concentric cylinders 22and 23, respectively,

welded to two end plates 24 and 25.

Cylinder 22 has a'diameter of 2 inches and cylinder 23 has a diameter of3 inches; the length of the cylinders between the end ;'plates is 8 /2inc-hes. End plate 24 has a central opening 26 into which the atomizinghead is inserted. End plate '25 has a one (1) inch opening 27 covered bya baffle plate 28 mounted in front of it to prevent direct blast offlame on the test specimen 29. Opening 27 in end plate 25 dischargesinto -a smaller cylinder 3-0 having a diameter of 1% inches and a lengthof 6 inches. The specimen 29 is mounted near the downstream end of thecylinder approximately 1% inches from the outlet thereof. Combustion airis introduced by means of air inlet 31 into the annulus betweencylinders 22 and 23, thereby preheating the combustion air, and thenthrough three pairs of inch tangential air inlets 32 in the innercylinder 22. The first pair of air inlets is spaced A inch from endplate 24; the second pair inch from the first;and the third 3 inchesfrom the second. The additional heating required to bring the combustionproducts to test temperature is supplied by an electric heating coil 33surrounding the outer cylinder 23. The entire combustion assembly issurrounded by suitable insulation 34. The test specimen 29 is a metaldisc one inch .in diameter by 0.125 inch thick, with a hole in thecenter by means of which the specimen is attached to a tube 35containing thermocouples. The specimen and tube assembly are mounted ona suitable stand 36.

In conducting a test in the above-described apparatus, a weighed metalspecimen is exposed to the combustion products of a residual fuel oil,the specimen being maintained at a selected test temperature of, forexample, 1350", 1450 or 1550 F. by the heat of the combustion products.The test is usually run for a period of hours with the rate of fuel feedbeing /2 pound per hour and the rate of atomizing air feed being 2pounds per hour. The combustion air entering through air inlet 31 is fedat 25 pounds per hour. At the end of the test run the specimen isreweighed to determine the weight of deposits and is then "descaled witha conventional alkaline descaling salt in molten condition at 475 C.After descaling, the specimen is dipped in 6 N hydrochloric acidcontaining a conventional pickling inhibitor, and is then Washed, driedand weighed. The loss in weight of the specimen after descaling is thecorrosion loss.

Tests are conducted in the apparatus just described using a 25-20stainless steel as the test specimen. The tests are run for 100 hours ata temperature of 1450 F. under the conditions described above. Tests aremade With the fuel oil compositions of Examples I and IV,

with fuel oil composition similar to those of these examples butcontaining only one of the additives in varying proportions, and withthe uncompounded residual fuel oils of Examples I and II. The followingtable shows the corrosion and deposits obtained.

It will be seen from the above table that the zinc additives and thealkali metal additives unexpectedly coact to minimize corrosion anddeposits. This is surprising when it is considered that, although theindividual additives tend to reduce corrosion and deposits, they stillpermit considerable corrosion unless used in relatively large amounts.

Thus the use of a sodium additive alone in amounts yielding as much as 6atom weights of sodium per atom weight of vanadium still permitscorrosion, and the zinc additive used alone requires about 6 atomweights of zinc per atom weight of vanadium before minimizing corrosion.With the combination of additives disclosed, considerably smalleramounts of each additive can be employed and corrosion and deposits arenonetheless minimized to negligible amounts. Furthermore, the depositsare of a non-adherent powdery texture. Similar results to those shownfor the specific additives employed in the examples and in the abovetable are obtained when using the other zinc and alkali metal compoundsdisclosed.

A typical analysis of the 25-20 stainless steel employed in the testingdescribed is shown in the following table in percent by weight:

Resort may be had to such modifications and variations as fall withinthe spirit of the invention and the scope of the appended claims.

We claim:

1. A fuel composition comprising a uniform blend of a major amount of aresidual fuel yielding a corrosive vanadium-containing ash uponcombustion, an amount of a vanadium-free zinc compound yielding about 4atom weights of zinc per atom weight of vanadium in said fuel and anamount of a vanadium-free alkali metal compound yielding about 1 atomweight of alkali metal per atom weight of vanadium in said fuel.

2. The composition of claim 1, wherein the fuel is a solid residualpetroleum fuel.

3. A fuel composition comprising a major amount of a residual fuel oilyielding a corrosive vanadium-containing ash upon combustion, an amountof a vanadium-free of a vanadium-free sodium compound yielding about 1atom weight of sodium per atom weight of vanadium in said fuel oil.

4. A fuel composition comprising a major amount of a residual fuel oilyielding a corrosive vanadium-containing ash upon combustion, an amountof zinc oxide yielding about 4 atom weights of zinc per atom weight ofvanadium in said fuel oil and an amount of sodium naphthenate yieldingabout 1 atom weight of sodium per atom weight of vanadium in said fueloil.

5. A fuel composition comprising a major amount of a residual fuel oilyielding a corrosive vanadium-containing ash upon combustion, an amountof zinc oxide yielding about 4 atom weights of zinc per atom weight ofvanadium in said fuel oil and an amount of sodium carbonate yieldingabout 1 atom weight of sodium per atom weight of vanadium in said fueloil.

6. In a gas turbine plant in which a fuel oil containing vanadium isburned and which includes heat resisting metallic parts exposed to hotcombustion gases and liable to be corroded by the corrosivevanadium-containing ash resulting from combustion of said oil, themethod of reducing said corrosion which comprises introducing in saidplant upstream of said parts a small amount of a vanadium-free mixtureof a zinc compound and an alkali metal compound, the amount of said zinccompound being sufiicient to yield about 4 atom weights of zinc per atomweight of vanadium in said fuel, and the amount of said alkali metalcompound being sufficient to yield about 1 atom weight of alkali metalper atom weight of vanadium in said fuel.

References Cited in the file of this patent UNITED STATES PATENTS2,706,149 Brenneman Apr. 12, 1955 2,781,005 Taylor et al Feb. 12, 1957FOREIGN PATENTS 689,579 Great Britain Apr. 1, 1953 711,895 Great BritainJuly 14, 1954 744,141 Great Britain Feb. 1, 1956 745,621 Great BritainFeb. 29, 1956 759,826 Great Britain Oct. 24, 1956 761,378 Great BritainNov. 14, 1956 781,581 Great Britain Aug. 21, 1957

6. IN A GAS TURBINE PLANT IN WHICH A FUEL OIL CONTAINING VANADIUM ISBURNED AND WHICH INCLUDES HEAT RESISTING METALLIC PARTS EXPOSED TO HOTCOMBUSTION GASES AND LIABLE TO BE CORRODED BY THE CORROSIVEVANDIUM-CONTAINING ASH RESULTING FROM COMBUSTION OF SAID OIL, THE METHODOF REDUCING SAID CORROSION WHICH COMPRISES INTRODUCING IN SAID PLANTUPSTREAM OF SAID PARTS A SMALL AMOUNT OF A VANADIUM-FREE MIXTURE OF AZINC COMPOUND AND AN ALKALI METAL COMPOUND, THE AMOUNT OF SAID ZINCCOMPOUND BEING SUFFICIENT TO YIELD ABOUT 4 ATOM WEIGHTS OF ZINC PER ATOMWEIGHT OF VANADIUM IN SAID FUEL, AND THE AMOUNG OF SAID ALKALI METALCOMPOUND BEING SUFFICIENT TO YIELD ABOUT 1 ATOM WEIGHT OF ALKALI METALPER ATOM WEIGHT OF VANADIUM IN SAID FUEL.